1. Field
The embodiments relate to an apparatus and a method for spraying layers of organic devices. In particular, the embodiments to spraying layers having multiple components, which for example are not soluble in the same solvent.
2. Description of the Related Art
Spray coating serves as a low-cost polymer coating method for producing electronic devices, such as solar cells or photodiodes on an organic basis, as known, for example, from WO 2003/107453 and the publication by Doojin Vak, Seok-Soon Kim, Jang Jo, Seung-Hwan Oh, Seok-In Na, Juhwan Kim, and Dong-Yu Kima “Fabrication of organic bulk heterojunction solar cells by a spray deposition method for low-cost power generation”, APPLIED PHYSICS LETTERS 91, 081102 (2007). In particular in the area of solar cells and photodetectors, efficiencies are drastically increased by the combination of a donor material (absorber and hole transport component) and an acceptor material (electron acceptor and transport component) in the photo-active layer of the device. This active layer comprises a mixture (blend) of these two substances and is better known as a “bulk heterojunction”. The separation of the charge carriers takes place at the interfaces of the two materials that form within the overall volume of the layer. A precondition for such a blend is that the two materials are soluble in the same solvent. Consequently, the bulk heterojunction solution can be applied to the substrate by low-cost methods such as spin coating, blade coating, slit coating, dip coating, inkjet printing, doctor blading and gravure printing, etc.
However, there are materials that have promising electronic properties but are not soluble in the same solvent. It is consequently impossible to produce a bulk heterojunction solution from these materials. Normally, in this case two-layer systems (bilayers) are produced, which however must forgo the positive properties, such as higher efficiencies, of a bulk heterojunction.
A further problem that frequently occurs is the production of multiply stacked polymer layers (multilayers) which are soluble in the same solvent. In this case (for example tandem OLEDs, tandem OPDs or tandem solar cells), unfortunately, the aforementioned coating methods cannot be used, since the application of a layer re-dissolves the layer lying thereunder, since the material forming the following layer is applied in the same solvent.
A further disadvantage of the previously known methods is that, depending on the solvent and application method used, with these application methods the maximum layer thickness that can be produced is limited.